Access terminal-assisted time and/or frequency tracking

ABSTRACT

An access point (e.g., a femto cell) that is connected in an active call with an access terminal may cooperate with that access terminal or another access terminal to derive timing information from one or more neighboring access points (e.g., macro access points). In addition, an access point may cooperate with an idle access terminal to derive timing information from one or more neighboring access points. For example, an access terminal may determine the difference between pilot transmission timing or frame transmission timing of a femto cell and a macro cell, and report this timing difference to the femto cell. Based on this timing difference, the femto cell may adjust the timing and/or frequency of its transmissions so that these transmissions are synchronized in time and/or frequency as per network operation requirements.

CLAIM OF PRIORITY

This application claims the benefit of and priority to commonly ownedU.S. Provisional Patent Application No. 61/262,091, filed Nov. 17, 2009,and U.S. Provisional Patent Application No. 61/299,837, filed Jan. 29,2010, the disclosure of each of which is hereby incorporated byreference herein.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to concurrently filed and commonly ownedU.S. patent application Ser. No. 12/947,039, entitled “IDLE ACCESSTERMINAL-ASSISTED TIME AND/OR FREQUENCY TRACKING,” the disclosure ofwhich is hereby incorporated by reference herein.

BACKGROUND

Field

This application relates generally to wireless communication and morespecifically, but not exclusively, to time tracking and/or frequencytracking.

Introduction

A wireless communication network may be deployed over a geographicalarea to provide various types of services (e.g., voice, data, multimediaservices, etc.) to users within that geographical area. In a typicalimplementation, macro access points (e.g., each of which providesservice via one or more macro cells) are distributed throughout a macronetwork to provide wireless connectivity for access terminals (e.g.,cell phones) that are operating within the geographical area served bythe macro network.

As the demand for high-rate and multimedia data services rapidly grows,there lies a challenge to implement efficient and robust communicationsystems with enhanced performance. To supplement conventional networkaccess points (e.g., to provide extended network coverage),small-coverage access points (e.g., low power access points) may bedeployed to provide more robust indoor wireless coverage or othercoverage to access terminals inside homes, enterprise locations (e.g.,offices), or other locations. Such small-coverage access points may bereferred to as, for example, femto cells, femto access points, homeNodeBs, home eNodeBs, or access point base stations. Typically, suchsmall-coverage access points are connected to the Internet and themobile operator's network via a DSL router or a cable modem. Forconvenience, small-coverage access points may be referred to as femtocells or femto access points in the discussion that follows.

Typically, femto cells transmit their signals with a certain time andfrequency accuracy as mandated by the relevant air interfacespecification. For example, in cdma2000 systems, all access points (basestations) are required to be synchronized to the “system time.” This“system time” is synchronous to coordinated universal time (UTC) (exceptfor leap seconds) and uses the same time of origin as global positioningsystem (GPS) time, within some small error.

Time and frequency synchronization amongst different access points ofthe network is required for several purposes including, for example,controlling inter-access point interference (which would otherwise ariseif different access points transmitted with widely differentfrequencies), and ensuring successful hand-off of an access terminal(mobile station) from one access point to another. If a femto cell isable to track the timing of nearby macro cells, the femto cell maycoordinate its beacon transmissions with the wake-up time of the accessterminals that are camped on the macro cell. This allows efficient femtocell idle-mode discovery and reduces the interference that wouldotherwise be induced at macro access terminals as a result of the femtocell beacon transmissions.

Current techniques used by femto cells for time and frequency trackinginclude deriving timing from a GPS receiver, deriving timing from acentral accurate clock using Internet Protocol (IP) techniques such asIEEE1588, deriving timing from terrestrial TV broadcasts, and sniffingsignals from neighboring macro access points. However, these techniqueshave several drawbacks. For example, a GPS receiver is not ideal for alow-cost consumer device such as a femto cell. Furthermore, a GPS signalmay not be available in typical femto cell deployment scenarios such asinside buildings, basements, warehouses, etc. To avoid some of thedrawbacks inherent to the use of GPS-based timing, a femto cell mayinstead rely on neighboring macro access points for time and frequencysynchronization. In this case, a femto cell sniffs a neighboring macroaccess point's forward link (FL) transmissions (e.g., using a specialmodule known as Network Listen Module) and uses the FL waveformstructure as well as messages sent by the macro access point to derivetiming and frequency information. However, to sniff neighboring macroaccess points that are transmitting in the same frequency band/channelas the femto cell, the femto cell transmitter is shut down so that femtocell forward link (FL) transmission do not interfere with the ability ofthe femto cell to receive macro access point FL transmissions.Therefore, such a Network Listen Module-based time and frequencytracking technique is used only when there is no user currently beingserviced by the femto cell (e.g., there is no active voice/data sessionon-going on the femto cell) on the carrier frequency (and potentiallyadjacent carrier frequencies) to be sniffed by the Network ListenModule. In view of the above, there is a need for more efficient andreliable mechanisms for providing time and frequency synchronization foraccess points.

SUMMARY

A summary of several sample aspects of the disclosure follows. Thissummary is provided for the convenience of the reader and does notwholly define the breadth of the disclosure. For convenience, the termsome aspects may be used herein to refer to a single aspect or multipleaspects of the disclosure.

The disclosure relates in some aspects to access terminal-assisted timeand frequency tracking for access points. For example, an access point(e.g., a femto cell) may cooperate with one or more access terminals toderive timing information from one or more neighboring access points(e.g., macro access points).

In some aspects, the derivation of this timing information may involvean access terminal determining the difference between the pilottransmission timing or the frame transmission timing of the access pointand a neighboring access point. The access terminal reports this timingdifference to the access point and the access point adjusts the timingand/or frequency of its transmissions based on this timing difference.As a result, these transmissions will track the timing of transmissionsby the neighboring access point (e.g., synchronize the phase of theaccess point's transmissions to the phase of the neighboring accesspoint's transmissions) and/or track a designated frequency (e.g.,synchronize to the transmit frequency used by the neighboring accesspoint in a case where the access points use the same carrier frequency,or synchronize to a frequency specified by network operationrequirements in a case where the access points do not use the samecarrier frequency). In some implementations, the neighboring accesspoint may be synchronized to “system time” (e.g., through the use ofGPS-based timing). Consequently, by tracking the neighboring accesspoint, the access point may synchronize to “system time” and therebymeet network timing requirements. In addition to meeting timingrequirements, by tracking the neighboring access point, the access pointmay also synchronize its frequency to and thereby meet network frequencysynchronization requirements. In other implementations, the neighboringaccess point may not have its timing synchronized to other access pointsof the network, but will have only its frequency synchronized to theseother access point. In these implementations, by tracking the frequencyof a neighboring access point, the access point may synchronize itsfrequency to the frequency used by the other access points in thenetwork.

Another use case of time tracking in accordance with the teachingsherein is to align access point (e.g., femto cell) beacon transmissionsor other transmissions to events that are based on the timing of atiming source (e.g., a neighboring macro cell). For example, idlereselection beacon transmissions of an access point (e.g., a femto cell)may be aligned with the wake-up time of an access terminal on aneighboring access point (e.g., a macro access terminal that is idlingon a macro cell). The access terminal wake-up time is derived from thetiming of the neighboring access point (e.g., the macro cell timing).Thus, by synchronizing its timing to the neighboring access point, theaccess point (e.g., the femto cell) may transmit beacons during anaccess terminal's expected wake-up times.

In some aspects, such an access terminal-assisted time and frequencytracking scheme may be advantageously employed when other time andfrequency tracking methods are not available. For example, the disclosedtracking scheme does not require access point transmissions to be shutdown to acquire timing information. Consequently, this tracking schememay be employed when an access point is handling an active call (e.g.,when a dedicated channel is established between the access point and anaccess terminal).

The disclosure thus relates in some aspects to a time and/or frequencytracking scheme where an access point that is connected in an activecall with an access terminal cooperates with that access terminal oranother access terminal to derive timing information from at least oneother access point. In some aspects, such a scheme may involvedetermining that an access point is handling an active call, acquiringtiming information from an access terminal during the active call as aresult of the determination that the access point is handling the activecall, and adjusting a clock that controls transmissions by the accesspoint, wherein the adjustment of the clock is based on the acquiredtiming information.

The disclosure also relates in some aspects to a time and/or frequencytracking scheme where an access point cooperates with at least onenearby idle access terminal to derive timing information from at leastone other access point. Here, an access point may receive timinginformation from, for example, an idle access terminal that is campingon the access point (e.g., listening to the access point's pagingchannel and other overhead channel transmissions) or from an accessterminal that supports other states where observed time difference (OTD)or other suitable timing information is reported. In some aspects, sucha scheme may involve determining that an access terminal is in idle modeat an access point, acquiring timing information from the accessterminal as a result of the determination that the access terminal is inidle mode, and adjusting a clock that controls transmissions by theaccess point, wherein the adjustment of the clock is based on theacquired timing information.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other sample aspects of the disclosure will be described inthe detailed description and the appended claims that follow, and in theaccompanying drawings, wherein:

FIG. 1 is a simplified block diagram of several sample aspects of acommunication system where an access point employs accessterminal-assisted time tracking and/or and frequency tracking;

FIG. 2 is a flowchart of several sample aspects of operations that maybe performed in conjunction with an access point that is handling anactive call acquiring timing information from an access terminal;

FIG. 3 is a flowchart of several sample aspects of operations that maybe performed in conjunction with an access point acquiring timinginformation from an idle access terminal;

FIG. 4 is a flowchart of several sample aspects of operations that maybe performed in conjunction with an access point sending a request to anaccess terminal for timing information;

FIG. 5 is a simplified diagram illustrating a sample pilot timingdifference as determined by an access terminal;

FIG. 6 is a flowchart of several sample aspects of operations that maybe performed in conjunction with adjusting an access point clock basedon pilot timing information acquired from an access terminal;

FIG. 7 is a simplified diagram illustrating a sample frame timingdifference as determined by an access terminal;

FIG. 8 is a flowchart of several sample aspects of operations that maybe performed in conjunction with adjusting an access point clock basedon frame timing information acquired from an access terminal;

FIG. 9 is a flowchart of several sample aspects of operations that maybe performed in conjunction with an access point determining a frequencyadjustment based on timing information received from an access terminal;

FIG. 10 is a flowchart of several sample aspects of operations that maybe performed in conjunction with an access point acquiring timinginformation associated with at least one timing source from at least oneaccess terminal;

FIG. 11 is a flowchart of several sample aspects of operations that maybe performed in conjunction with an access point acquiring timinginformation from an access terminal at a specified rate;

FIG. 12 is a flowchart of several sample aspects of operations that maybe performed in conjunction with an access point electing to acquiretiming information from a timing source if the timing source hassufficiently accurate timing;

FIG. 13 is a flowchart of several sample aspects of operations that maybe performed in conjunction with an access point weighting timinginformation from different timing sources based on the reliability ofthe timing sources;

FIG. 14 is a simplified block diagram of several sample aspects ofcomponents that may be employed in communication nodes;

FIG. 15 is a simplified diagram of a wireless communication system;

FIG. 16 is a simplified diagram of a wireless communication systemincluding femto nodes;

FIG. 17 is a simplified diagram illustrating coverage areas for wirelesscommunication;

FIG. 18 is a simplified block diagram of several sample aspects ofcommunication components; and

FIGS. 19-21 are simplified block diagrams of several sample aspects ofapparatuses configured to provide time tracking and/or frequencytracking as taught herein.

In accordance with common practice the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may be simplified for clarity. Thus,the drawings may not depict all of the components of a given apparatus(e.g., device) or method. Finally, like reference numerals may be usedto denote like features throughout the specification and figures.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. It should beapparent that the teachings herein may be embodied in a wide variety offorms and that any specific structure, function, or both being disclosedherein is merely representative. Based on the teachings herein oneskilled in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. Furthermore,an aspect may comprise at least one element of a claim.

FIG. 1 illustrates several nodes of a sample communication system 100(e.g., a portion of a communication network). For illustration purposes,various aspects of the disclosure will be described in the context ofone or more access terminals, access points, and network entities thatcommunicate with one another. It should be appreciated, however, thatthe teachings herein may be applicable to other types of apparatuses orother similar apparatuses that are referenced using other terminology.For example, in various implementations access points may be referred toor implemented as base stations, NodeBs, eNodeBs, femto cells, and soon, while access terminals may be referred to or implemented as userequipment, mobile stations, and so on.

Access points in the system 100 provide access to one or more services(e.g., network connectivity) for one or more wireless terminals (e.g.,access terminal 102) that may be installed within or that may roamthroughout a coverage area of the system 100. For example, at variouspoints in time the access terminal 102 may connect to an access point104, an access point 106, an access point 108, or some access point inthe system 100 (not shown). Each of these access points may communicatewith one or more network entities (represented, for convenience, by anetwork entity 110) to facilitate wide area network connectivity.

These network entities may take various forms such as, for example, oneor more radio and/or core network entities. Thus, in variousimplementations the network entities may represent functionality such asat least one of: network management (e.g., via an operation,administration, management, and provisioning entity), call control,session management, mobility management, gateway functions, interworkingfunctions, or some other suitable network functionality. Also, two ofmore of these network entities may be co-located and/or two or more ofthese network entities may be distributed throughout a network.

Access points in the system 100 employ internal timing mechanisms tocontrol the timing and carrier frequency of wireless transmission andreception. For example, by transmitting and receiving at specified timeson a specified frequency (or frequencies), an access point may be ableto more efficiently communicate with other wireless entities (e.g.,access terminals) in the network and may be able to reduce theinterference that the access point's transmission may otherwise cause atother wireless entities (e.g., at access terminals connected to otheraccess points). As mentioned above, one technique for facilitatingefficient communication and mitigating interference involves requiringaccess points to be synchronized to the “system time” in a network. Insuch a case, access points may transmit their respective signals atspecified timing offsets from a known “system time” (e.g., time T0). Inaddition, access points should also transmit on specified carrierfrequencies to avoid interfering with transmission of other accesspoints. An error in transmit frequency can also interfere withtransmissions on neighboring carrier frequencies.

Consequently, signals transmitted by such access points may provide anindication of the internal timing used by each access point. Forexample, an access point may transmit a pilot signal sequence beginningat a specified timing offset from time T0. Similarly, an access pointmay transmit a frame beginning at a specified timing offset from timeT0. In the example of FIG. 1, the access point 104, the access point106, the access point 108 may transmit signals (e.g., pilots and/orframes) that provide an indication of the internal timing used by eachaccess point as represented by the dashed arrows 112, 114, and 116,respectively.

The access point 104 (e.g., a femto cell employing a relatively low costtiming source) includes the capability to use access terminal-assistedtime tracking and/or frequency tracking Such an access terminal-assistedtracking scheme may be employed when the access point 104 is servicingan active call and/or when the access point 104 detects an idle accessterminal.

For example, when the access point 104 is not servicing an active call,the access point 104 may employ a Network Listen Module (not shown) thatreceives signals 114 and 116 from nearby access points 106 and 108 thathave highly accurate timing (e.g., GPS-based) timing. Based on thetiming information provided by these signals, the access point 104synchronizes its timing (e.g., adjusts the phase and/or frequency of aninternal clock) with the timing of the access points 106 and 108. Whenthe access point 104 is handling an active call, however, the accesspoint 104 may switch to access terminal-assisted time tracking and/orfrequency tracking To this end, the access point 104 includes anactive/idle mode detection component 122 that detects when the accesspoint is handling an active call and invokes a switch to the accessterminal-assisted tracking scheme. Upon switching to this trackingscheme, the access point 104 may then cooperate with the access terminalinvolved in the active call or some other nearby access terminal toacquire timing information indicative of the timing of nearby accesspoints.

For the situation where an access terminal is idling on the access point104, the active/idle mode detection component 122 may detect thepresence of the nearby idle access terminal by, for example, sending amessage to the access terminal requesting the access terminal tore-register at the access point 104 or requesting the access terminal torespond to a control channel message sent by the access point 104. Uponreceiving a registration message or response from the access terminal,the access point 104 may then cooperate with the access terminal toacquire timing information indicative of the timing of nearby accesspoints.

In either the active call situation or the idle access terminalsituation, an access terminal 102 in the vicinity of the access points104, 106, and 108 may receive the signals 112, 114, and 116 from theseaccess points and generate timing information based on the thesesignals. For example, a timing information generation component 118 maycalculate the timing difference between the times at which the signals112 and 114 are received at the access terminal. Alternatively, or inaddition, the timing information generation component 118 may calculatethe timing difference between the times at which the signals 112 and 116are received at the access terminal. After generating this timinginformation, the access terminal 102 sends the timing information to theaccess point 104 as represented by the dashed arrow 120. This timinginformation is sent in response to a request (or requests) by the accesspoint 104 or may be sent when certain other events (e.g., channelquality of transmission from one or more access points falls below orexceeds some threshold).

A time and/or frequency tracking component 124 of the access point 104uses this timing difference information to determine how far off thetiming (and/or frequency) of the access point 104 is from the timing(and/or frequency) of another access point (e.g., access point 106and/or access point 108). For example, based on the acquired timinginformation, the time and/or frequency tracking component 124 maydetermine the time difference (e.g., in chips, fractions of chips, etc.)between the T0 being used by the access point 104 and the T0 being usedby the access point 106. The time and/or frequency tracking component124 then adjusts its internal timing reference (e.g., adjusts the phaseand/or frequency of an internal clock) to track the timing (and/orfrequency) of the access point 106 based on this time difference.

As another example, access point beacon transmissions or othertransmissions may be aligned to events that are based on the timing of atiming source. In this case, the timing information received from theaccess terminal 102 is indicative of the timing of an event at theaccess terminal 102. For example, idle reselection beacon transmissionsof the access point 104 may be aligned with the wake-up time of theaccess terminal 102. This wake-up time may be derived from the timingof, for example, the access point 106 (e.g., when the access terminal102 is idling on the access point 106). Thus, by synchronizing itstiming to the neighboring access point, the access point (e.g., thefemto cell) may transmit beacons during an access terminal's expectedwake-up times. Thus, in some aspects, the timing information receivedfrom the access terminal 102 is indicative of timing of another accesspoint (e.g., the access point 106) or a timing source, which drivestiming of an event at the access terminal 102; and the adjustment of theclock comprises adjusting timing of a signal transmission by the accesspoint 104 so that the adjusted timing is synchronized with the timing ofthe event.

Various techniques may be employed to facilitate efficient and effectiveaccess terminal-assisted tracking operations in accordance with theteachings herein. For example, as described below, an access point mayadjust its internal clock based on timing information associated withone or more timing sources (e.g., access points) received from one ormore access terminals. To this end, the access point may send messagesto one or more access terminals requesting timing information fromspecified timing sources, requesting that the access terminals acquirethe timing information from one or more specified carrier frequencies(e.g., the same carrier frequency used by the access point and/or atleast one other carrier frequency). Also, the access point may determinewhether to use timing information associated with a particular timingsource based on the accuracy of that timing source and/or the signalquality of this access point as reported by the access terminal alongwith timing information. For example, if an access terminal reportstiming information for two macro cells, the access point may elect touse the timing information associated with the macro cell with thestrongest received signal strength (as measured and reported by theaccess terminal via a PSMM, RUM, etc.).

These and other access terminal-assisted tracking operations will bedescribed in more detail in conjunction with the flowcharts of FIGS.2-4, 6, and 8-14. For convenience, the operations of FIGS. 2-4, 6, and8-14 (or any other operations discussed or taught herein) may bedescribed as being performed by specific components (e.g., thecomponents of FIG. 1 and FIG. 14). It should be appreciated, however,that these operations may be performed by other types of components andmay be performed using a different number of components. It also shouldbe appreciated that one or more of the operations described herein maynot be employed in a given implementation.

FIG. 2 illustrates sample operations that may be performed at an accesspoint in conjunction with switching to access terminal-assisted trackingwhen the access point is handling an active call. For purposes ofillustration, in some aspects the following describes a scenario wherean access point cooperates with a nearby access terminal to track timingof at least one nearby macro access point during the active call. Itshould be appreciated that other timing sources (e.g., pico cells, femtocells, etc.) may provide a sufficiently accurate timing source in otherscenarios.

As represented by block 202, the access point may use a default timetracking and/or frequency tracking scheme when the access point is nothandling any active calls. For example, the access point may employ aNetwork Listen Module that sniffs (e.g., turns on a receiver to acquire)signals from at least one nearby macro access point and acquire timinginformation from those signals. As discussed above, the access point maydisable some or all of its transmissions during this sniffing operation.Once the timing information is acquired, the access point adjusts aclock that controls transmissions by the access point. In accordancewith the teachings herein, this adjustment is based on the acquiredtiming information so that the access point maintains time and/orfrequency synchronization with the at least one nearby macro accesspoint.

As represented by block 204, at some point in time, the access pointdetermines that it is handling an active call. For example, an accessterminal idling on the access point may initiate a call through theaccess point, or the access point may receive a call destined for anaccess terminal idling on the access point.

As represented by block 206, as a result of the determination that theaccess point is handling an active call, the access point commencesacquiring timing information from an access terminal during the activecall. That is, the access point temporarily switches to accessterminal-assisted time tracking and/or frequency tracking to receivetiming information associated with one or more timing sources (e.g.,access points) from an access terminal (e.g., the access terminalinvolved in the active call or some other access terminal). Oneadvantage of using an access terminal (e.g., an active or idle accessterminal) for time and/or frequency tracking here is that the accesspoint may acquire timing information without using a Network ListenModule. Hence, complexities associated with the use of a Network ListenModule (e.g., shutting down access point transmissions) may be avoided.

As discussed in more detail below, this timing information may takevarious forms and be acquired in various ways. For example, the accessterminal may report pilot timing difference information via a cdma2000pilot strength measurement message (PSMM), a cdma2000 candidatefrequency search report message (CFSRPM), a UMTS measurement reportmessage (MRM), a 1×EV-DO route update message (RUM), or via another typeof message used by some other type of radio technology. This pilottiming difference information may be indicative of, for example, a phasedifference between a pilot signal received by the access terminal fromthe access point and a pilot signal received by the access terminal froma macro access point.

The access terminal may report frame timing difference information via,for example, a UMTS observed time difference (OTD) report or via anothertype of message used by some other type of radio technology. This frametiming phase difference information may be indicative of, for example,the difference between a time at which a frame from the access point isreceived by the access terminal and a time at which a frame from a macroaccess point is received by the access terminal. For example, an accessterminal may send a system frame number-connection frame number(SFN-CFN) OTD report to its serving cell to report the time differencebetween the serving cell and a neighbor cell (e.g., the timingdifference between the times at which frames are received from thedifferent cells). As another example, an idle access terminal may sendan OTD report to report the time difference between two cells (e.g., thetiming difference between the times at which frames are received fromthe different cells). Here, an access terminal may send a system framenumber-system frame number (SFN-SFN) OTD report (Type 1 or Type 2) whenthe access terminal is in idle mode or in some other state where OTDreports are supported.

The SFN-CFN OTD and/or the SFN-SFN OTD may be used for time and/orfrequency tracking at an access point (e.g., a femto cell) as discussedbelow. This method is applicable to all access terminal states that aresupported for these measurement reports. For example, an access terminalmay send an SFN-SFN OTD Type 1 report in the following states: Idlemode, URA_PCH intra, CELL_PCH intra, or CELL_FACH intra. In addition, anaccess terminal may send an SFN-SFN OTD Type 2 report in the followingstates: URA_PCH intra, URA_PT inter, CELL_PCH intra, CELL_PCH inter, orCELL_FACH intra, CEL_FACH inter, CELL_DCH intra, or CELL_DCH inter.

Typically, the access point sends a request to the access terminal forthis timing information. In some cases, however, the access point mayacquire timing information that the access terminal sends without beingrequested to do so. For example, an access terminal may send a PSMM or aMRM that is triggered by certain signal conditions at the accessterminal. As another example, the access terminal may send measurementsperiodically.

As represented by block 208, the access point adjusts a clock thatcontrols transmissions by the access point based on the acquired timinginformation. For example, the access point may process the receivedtiming information to determine the timing difference between T0 at theaccess point and T0 at a nearby macro access point. The access point maythen adjust its clock based on this timing difference.

The adjustment of the clock may involve time tracking and/or frequencytracking. For example, in a cdma2000 system, the access point mayperform time and frequency tracking. In addition, in some cases onlyfrequency tracking may be employed in a UMTS system, while in othercases time and frequency tracking may be employed in a UMTS system.

As an example of time tracking, in the event the access point determinesthat its clock lags the clock of the macro access point by a certainamount of time (e.g., expressed as a number of chips), the access pointmay adjust the phase of its clock by that amount of time. In this way,the phase of a signal transmitted by the access point is adjusted sothat the adjusted phase tracks (e.g., is synchronized with) the phase ofthe timing source used by the macro access point (within somepermissible error margin).

As an example of frequency tracking, in the event the access pointdetermines that the frequency of its clock differs from the frequency ofthe clock of the macro access point by a certain frequency deviation(e.g., as determined based on timing differences reported by the accessterminal over a period of time), the access point may adjust thefrequency of its clock by that frequency deviation. In this way, thefrequency of a signal transmitted by the access point is adjusted sothat the adjusted frequency matches the specified (i.e., the designatedcarrier) frequency within some permissible error margin (here,designated means the frequency at which the access point should transmitin accordance with the operational requirements of the network). Incases where the access point and macro access point operate on the samecarrier frequency, this may involve the access point synchronizing itstransmit frequency with a transmit frequency of the macro access point.In cases where the access point and macro access point do not operate onthe same carrier frequency, this may involve the access point matching afrequency required by the network. Here, the access point may acquirethe required frequency based on a transmit frequency used by the macroaccess point.

As represented by block 210, the access point may return to using thedefault time tracking and/or frequency tracking scheme once the accesspoint is no longer handling any active calls. For example, upondetermining that the access point is no longer handling an active call,the access point may recommence the use of a Network Listen Module,re-attempt acquisition of GPS-based timing if the access point includesGPS capability (e.g., which may be intermittently available if theaccess point is located within a building), or recommence use of someother mechanism to provide time and frequency tracking.

In addition, while using the default tracking mechanism, the accesspoint may acquire information that is used for calibrating the accessterminal-assisted tracking. For example, when the access point issynchronized to the timing of a macro access point, the access point maydetermine the propagation time between the access point and the macroaccess point. This information may then be used during accessterminal-assisted tracking to, for example, calculate the timing offsetbetween access points as discussed below.

FIG. 3 illustrates sample operations that may be performed at an accesspoint that cooperates with a nearby idle access terminal to synchronizeto at least one timing source (e.g., a nearby macro access point). Theseoperations may be performed independently (e.g., to acquire timinginformation whenever an idle access terminal is near the access point),or in conjunction with switching to access terminal-assisted trackingwhen the access point is handling an active call (e.g., the access pointcooperates with an idle access terminal to acquire timing informationduring the active call). One advantage of using idle access terminalsfor time and/or frequency tracking is that the access point may acquiretiming information without using a Network Listen Module. Hence,complexities associated with the use of a Network Listen Module (e.g.,shutting down access point transmissions) may be avoided.

As represented by block 302, at some point in time the access pointdetermines that a nearby access terminal is connected with the accesspoint in idle mode. Here, the access point may determine whether theaccess terminal is idling on the access point (i.e., the access terminalis periodically monitoring the access point's FL paging channel) by, forexample, sending a message to the access terminal that requests theaccess terminal to re-register at the access point. Receipt of aregistration message from the access terminal may thus confirm that theaccess terminal is idling on the access point. As another example, theaccess point may send a message to the access terminal that requests theaccess terminal to respond to (e.g., acknowledge) a message the accesspoint sends on a control channel (e.g., a paging channel). Again, thereceipt of an appropriate response from the access terminal may confirmthat the access terminal is idling on the access point.

As represented by block 304, in some cases, the access point also maysend a message to the access terminal to cause the access terminal toreport timing information to the access point. For example, the accesspoint may send a message that explicitly requests the access terminal tosend timing information. In response to such a request, the accessterminal may send timing information in a dedicated message or mayinclude the timing information in some other message that issubsequently sent to the access point. As another example, the accesspoint may send a message that does not include such an explicit requestbut that may nonetheless result in the access terminal sending timinginformation. For example, a message that requests the access terminal toregister (e.g., periodically register) with the access point may causethe access terminal to perform registration, where as a matter of coursethe access terminal provides timing information whenever it registers atan access point.

In some cases, the access point may not need to send the message ofblock 304 to the access terminal. For example, the sending of a messageat block 302 that determines that the access terminal is idling on theaccess point may cause the access terminal to send timing information tothe access point.

As represented by block 306, the access terminal sends a messageincluding timing information to the access point. This timinginformation may take various forms and may be sent in various ways indifferent implementations. For example, in a 1×EV-DO system, the accesspoint may send a route update message (RUM) that includes timinginformation relating to neighboring access points. As another example,as discussed above, an access terminal may send an SFN-SFN OTD report(Type 1 or Type 2) when the access terminal is in idle mode or in someother state where OTD reports are supported. Such a report may be sentvia, for example, a measurement report message (MRM).

As yet another example, in a cdma2000 system, the access terminal maysend a radio environment report message (RERM) that includes pilot phaseinformation of neighboring access points that are on the same carrierfrequency as the access point's FL carrier frequency. RERMs may be sent,for example, upon request as discussed herein or upon the occurrence ofcertain events (e.g., a registration attempt or a page response by theaccess terminal). Thus, as discussed above, the access point may requestan idle mobile to repeatedly (e.g., periodically) register with theaccess point and, as a result, the access point may repeatedly receiveRERMs from the access terminal.

As represented by block 308, the access point thus acquires timinginformation from an access terminal as a result of the determinationthat the access terminal is in idle mode. For example, upon receiving aRERM that includes macro phase information, the access point may usethis information to determine how to adjust its clock for time and/orfrequency tracking as described herein.

Accordingly, as represented by block 310, the access point adjusts itsclock based on the acquired timing information. The operations of block310 are thus similar to the operations described above at block 208.

Referring now to FIGS. 4-14, additional operations that may be performedto facilitate access terminal-assisted time and/or frequency trackingwill now be described. In general, the operations described below may beused in a case where an access point invokes access terminal-assistedtracking during an active call, or in a case where an access point doesnot use this condition to invoke access terminal-assisted tracking(e.g., in a case where access terminal-assisted tracking is invoked whenan access point detects a nearby idle access terminal).

Referring to FIG. 4, as mentioned above, an access point may specifycertain aspects of how an access terminal provides timing information.For example, an access point may specify when timing information is tobe provided, how often timing information is to be provided, the timingsource of the timing information, and so on. Also, an access point mayuse idle periods in the down link (IPDL) to improve the accuracy of theaccess terminal reporting (e.g., pilot-based reports or OTD reports).

As represented by block 402, at some point in time, the access point maydetermine information that may be used by access terminals for obtainingtiming information. This information may include, for example, a list ofaccess points from which timing information is to be obtained (e.g., alist of identifiers of access points that are known to have highlyaccurate timing), a list of pilots for which the access terminal is tosearch (e.g., a list of PN offsets associated with known access points),a list of carrier frequencies on which the access terminal is to searchfor signals (e.g., which may or may not include the carrier frequencybeing used by the access point). In some implementations, this controlinformation may take the form of a Neighbor List.

The above information may be determined in various ways. For example,the access point may receive this information from the network (e.g.,from a configuration entity in the network), or the access point maylearn this information over time. As a specific example, the corenetwork may provision an access point with a list of neighboring accesspoints via the backhaul. Alternatively, the access point may discoverits neighborhood on its own through the use of a Network Listen Moduleor some other suitable mechanism.

As represented by block 404, at some point in time, accessterminal-assisted time and/or frequency tracking is triggered at theaccess point. For example, as discussed above, this type of tracking maybe commenced upon determining that the access point is handling anactive call or upon detecting an idle access terminal at the accesspoint.

As represented by block 406, in conjunction with commencing accessterminal-assisted time and/or frequency tracking, the access point sendsa request for timing information to the access terminal. For example,the access point may send a message including a specific request fortiming information and including the control information described aboveat block 402. In some other cases, the request for timing informationmay not be made explicitly, but timing information may still be obtainedby requesting some other information (e.g., signal strengths of otheraccess points). When the access terminal sends back this information,timing information may also be included by default along with signalstrength information.

As represented by block 408, the access terminal obtains timinginformation in the specified manner and sends the timing information tothe access point. An example of a scenario where the access pointcomprises a femto cell and the neighboring access point comprises amacro cell follows.

As mentioned above, time and frequency tracking information may bederived from a macro access point that is operating on the same carrierfrequency as the femto cell's operating carrier frequency or a differentcarrier frequency. When a macro access point shares the femto cell's FLcarrier frequency, reporting such as PSMM reporting may be used toobtain the macro phase information. If the macro access point frequencyis different from the femto cell's FL carrier frequency, then the femtocell may request the access terminal to search on at least one otherfrequency by sending a candidate frequency search request command. Asdiscussed herein, the macro PNs to search as well as the searchperiodicity may be specified by the femto cell. In an inter-frequencysearch scenario, the access terminal intermittently tunes away from thefemto cell's FL carrier frequency to search for macro pilots on thespecified frequency or frequencies and reports back macro pilot strengthand phase using a signaling message such as a candidate frequency searchreport message (CFSRPM).

As represented by block 410, the access point receives the timinginformation sent by the access terminal. For example, the femto celldescribed above may use the macro phases reported in the CFSRPM or someother message to obtain information for time and frequency tracking.

As represented by block 412, the access point determines a clockadjustment based on the acquired timing information. For example, asdiscussed at FIGS. 5-8, the timing information provided by the accessterminal may simply provide timing information from the perspective ofthe access terminal (e.g., a difference in signal arrival times). Thistiming information may then need to be processed further to determinehow much the clock at the access point is to be adjusted.

As represented by block 414, the access point adjusts its clock based onthe determined clock adjustment. For example, if the clock adjustmentindicates a phase differential, the access point adjusts the phase ofthe clock by the specified amount (e.g., a specified number of chips).In addition, if the clock adjustment indicates a frequency differential,the access point adjusts the frequency of the clock by the specifiedamount (e.g., a specified frequency shift).

The timing information acquired by an access point via an accessterminal may take various forms. FIGS. 5-8 describe two examples wheretiming information is based on received pilot timing (FIGS. 5 and 6) andwhere timing information is based on received frame timing (FIGS. 7 and8). It should be appreciated that timing information may be derived inother ways in other implementations.

For purposes of illustration, FIGS. 5 and 6 will be described, in part,in the context of a 1×RTT system where the serving access pointcomprises a femto cell and the neighboring access point comprises amacro cell. It should be appreciated, however, that these concepts maybe applicable in other technologies as well.

In accordance with conventional practice, an access terminal in anactive call with a macro cell or a femto cell continuously searches forother neighboring access points so that handoff may be performed to anyof these neighboring access points, if needed. When the current servingaccess point (e.g., the access point with which the access terminal hasan active call) FL signal quality is below a certain threshold and/orthe neighboring access point FL signal quality is above a certainthreshold, the access point reports the neighboring access point to theserving access point using a PSMM. The PSMM contains the pilot strengthand the pilot phase of the neighboring access point relative to theserving access point. The access point timing typically is locked (e.g.,synchronized) to the earliest arriving path from the serving accesspoint. The phase difference between the earliest arriving path from theneighboring access point and the earliest arriving path from the servingaccess point is thus reported in the PSMM.

In accordance with the teachings herein, if the serving cell knows thatthe neighboring access point has accurate time and frequencysynchronization (e.g., GPS-based timing), the serving access point mayuse the PN phase of the neighboring access point reported by the accessterminal (e.g., the access terminal in the active call) via the PSMM toprovide time and frequency tracking Thus, the techniques describedherein may be advantageously employed at a serving access point thatdoes not have accurate time and frequency tracking Here, the accesspoint may use access terminal assistance to achieve tracking through theuse of measurements from a neighboring, non-serving access point.Moreover, the described techniques may be employed even when the servingand non-serving access points are operating on different carrierfrequencies by requesting the access terminal to search macro pilots ona different carrier frequency and reporting back information of macropilots on this frequency.

In a femto cell deployment, neighboring macro access points generallywill have very accurate time and frequency synchronization derived froma GPS receiver. Therefore, a femto cell may receive PSMM reportscontaining macro access point pilot phase information from an accessterminal (e.g., an active access terminal) and use that information fortime and frequency tracking.

FIG. 5 is a timing diagram that illustrates pilot-based timinginformation that an access terminal may send to an access point.Specifically, the time difference parameter D represents the timingdifference between the time at which the access terminal receives apilot signal from its serving access point and the time at which theaccess terminal receives a pilot signal from a neighboring access point.Thus, the parameter D represents the relative phase difference betweenthe femto cell and the macro cell. The parameter D may be reported, forexample, in a PSMM or CFSRPM.

For purposes of illustration, assume without loss of generality that thefemto cell FL frequency is F2, while a neighboring macro cell is onfrequency F1. Initially, when there is no active access terminalconnected to the femto cell, the femto cell synchronizes its time andfrequency using other means such as using a Network Listen Module withperiodic femto cell shutdown. Once an access terminal in active mode isconnected to the femto cell, the femto cell requests the access terminalto perform candidate frequency searches on the macro frequency F1. Uponreceiving the resulting search report, the femto cell obtains timing andfrequency tracking information as follows.

In FIG. 5, T0 represents the “system time” corresponding to PN offset=0.The macro cell PN offset is represented by PN_m, while the femto cell PNoffset is represented by PN_f. The parameter t2 represents thepropagation delay (one way delay) between the macro cell and the accessterminal for the earliest arrival path. The parameter t1 represents thepropagation delay (one way delay) between the femto cell and the accessterminal for the earliest arrival path. The parameter (c) represents thetiming error at the femto cell. Note that it is assumed that the macrocell accurately tracks “system time.”

The phase offset reported in the CFSRPM message corresponds to:D=(To+PN_f+e+t1)−(To+PN_m+t2)=(PN_f−PN_m)+(e+t1−t2). Here, the accessterminal can correctly search for the macro cell if the delay (e+t1−t2)is less than the search window used for searching the macro sectors.Also, the femto cell may accurately derive PN_m from the reported D aslong as (e+t1−t2) is less than 64*PILOT_INC (pilot increment parameter)used in the system.

Once the femto cell determines PN_m, the effective phase differencereported by the access terminal is: Deff=e+t1−t2. This phase differenceincludes the timing error (e) at the femto cell and timing delays due topropagation. Typically, in femto cell environments, t1 is less than 1chip. Similarly, in most macro networks, t2 is likely to be on the orderof a few chips (1 chip˜230 m propagation distance, thus a 2-3 chip delaymay cover very large macro cell sizes). Thus, the contribution of thepropagation delays is small and likely to be comparable to the timingerror (e). Consequently, the timing error may be estimated as theeffective macro phase Deff. This value may then be used by the femtocell to correct its timing (e.g., adjust its clock).

Additional mechanisms may be employed by the femto cell to learn t2, ifdesired. For example, the one way delay may be reported to the femtocell by the core network when an active access terminal performs ahandoff from the macro cell to the femto cell. Thus, the femto cell mayrecord an approximate value of t2 based on past handoffs, andsubsequently use this value to correct timing during accessterminal-assisted tracking.

Alternately, the core network may provide an approximate one way delayvalue to the femto cell based on information that the femto cell is inthe coverage region of a particular macro cell.

In another example, based on occasional availability of a GPS signal (inan implementation where a femto has GPS capabilities), the femto cellmay synchronize it's timing to GPS time, and then use the Network ListenMode or PSMMs to measure the received macro signal's PN phaseinformation. This information may then be subsequently used as the oneway propagation delay during access terminal-assisted tracking (e.g., inthe absence of a GPS signal).

In the above discussion, the presence of frequency error at the femtocell was ignored. In practice, frequency error will introduce timingdrift (i.e., the error (e) will vary with time). In such a case, theeffective reported macro phase may be written as:Deff(n)=e(n)+t1(n)−t2(n), where n is the time index.

In femto cell environments where users are stationary or walking at avery slow speed, t1(n) and t2(n) are not expected to vary with time.Thus, Deff(n) may be approximated as: Deff(n)=e(n)+t1−t2.

In the absence of any other errors related to estimating the receivedmacro signal's PN phase, the rate of change of this phase difference isequal to the frequency error. Thus, by requesting multiple CFSRPMs fromthe access terminal, the femto cell may use a robust algorithm todetermine its frequency error and compensate for the same, even in thepresence of errors related to estimating the received macro signal's PNphase.

With the above in mind, FIG. 6 describes sample operations for animplementation wherein timing information is based on received pilotsignal timing.

As represented by block 602, the access terminal receives pilot signalsfrom nearby access points. As discussed above, each of these pilotsignals may comprise a different PN code offset.

As represented by block 604, the access terminal determines a timingdifference between a first one of the access points (e.g., a servingfemto cell) and at least one other one of the access points (e.g., amacro cell). This may involve, for example, determining the parameter Das discussed above.

As represented by block 606, the access terminal sends the timingdifference information to the first access point. For example, theaccess terminal may send the parameter D via a PSMM or CFSRPM asdiscussed herein. The first access point receives this timing differenceinformation as represented by block 608.

As represented by block 610, the first access point determines itstiming error based on the received timing difference information. Thismay involve, for example, calculating or estimating the parameter (e) asdiscussed above.

As represented by block 612, the first access point adjusts a clock usedfor transmitting signals based on the determined timing error. Forexample, the first access point may adjust the phase of the clock basedon a single timing error value or based on several timing error valuesreceived from the access terminal over a period of time (e.g., bycalculating an average of the timing error values over a certainduration). Also, as discussed in more detail below, the first accesspoint may adjust the frequency of the clock based on the rate of changeof timing error values received from the access terminal over a periodof time.

FIGS. 7 and 8 illustrate an example of an implementation that employsframe-based timing information. For example, if it is known that aneighboring access point has accurate time and frequencysynchronization, then a serving access point may use the observed timedifference (OTD) reported by an access terminal in an active call, idlemode, or other supported states to provide time and/or frequencytracking. For example, a femto cell may use access terminal measurementreports containing the OTD between the femto cell and a macro cell fortime and/or frequency tracking.

FIG. 7 is a timing diagram that illustrates frame-based timinginformation that an access terminal (UE) may send to an access point. Ingeneral, the time difference parameter Tm represents the timingdifference between the time at which the access terminal receives aframe from its serving access point (e.g., a femto cell) and the time atwhich the access terminal receives a frame from another access point(e.g., a macro cell). For example, the parameter Tm may represent thetime difference (in units of chip) between the femto cell DL DPCH(dedicated physical channel) frame at the access terminal (e.g., a HomeUE) and the macro cell PCCPCH (primary common control physical channel)frame at the access terminal. This Tm value may be used by the femtocell for frequency and time tracking as discussed herein.

An example of an SFN-CFN OTD that includes Tm is as follows: SFN-CFNOTD=OFF×38400+Tm (See 3GPP TS25.215).

Here, Tm=(TUETx−T0)−TRxSFN, given in chip units with the range [0, 1, .. . , 38399] chips. TUETx is the time when the access terminal (UE)transmits an uplink DPCCH frame. The uplink DPCCH/DPDCH frametransmission takes place approximately T0 chips after the reception ofthe first detected path (in time) of the corresponding downlinkDPCCH/DPDCH or F-DPCH frame. T0 is a constant defined to be 1024 chips.TRxSFN is the time at the beginning of the neighboring P-CCPCH framereceived most recent in time before the time instant TUETx−T0 in theaccess terminal.

Also, OFF=(SFN−CFNTx) mod 256, given in number of frames with the range[0, 1, . . . , 255] frames. CFNTx is the connection frame number for theaccess terminal (UE) transmission of an uplink DPCCH frame at the timeTUETx. SFN is the system frame number for the neighboring P-CCPCH framereceived in the access terminal at the time TRxSFN. In theinter-frequency case, the access terminal is not required to read SFN(OFF is set to 0).

Similarly, SFN-SFN OTD may be used for time and frequency tracking whenthere is an access terminal in idle mode (or other supported states)with the femto cell. In this case: SFN-SFN OTD Type 1=OFF×38400+Tm (See3GPP TS25.215). A similar scheme may be employed for SFN-SFN OTD Type 2.

Here, Tm=TRxSFNj−TRxSFNi, given in chip units with the range [0, 1, . .. , 38399] chips. TRxSFNj is the time at the beginning of a receivedneighboring P-CCPCH frame from cell j. TRxSFNi is the time at thebeginning of the P-CCPCH frame from serving cell i of most recent intime before the time instant TRxSFNj in the access terminal (UE).

Also, OFF=(SFNi−SFNj) mod 256, given in number of frames with the range[0, 1, . . . , 255] frames. SFNj is the system frame number for downlinkP-CCPCH frame from cell j in the access terminal (UE) at the timeTRxSFNj. SFNi is the system frame number for the P-CCPCH frame fromserving cell i in the access terminal at the time TRxSFNi.

With the above in mind, FIG. 8 describes sample operations for animplementation wherein timing information is based on received frametiming.

As represented by block 802, the access terminal receives frames fromnearby access points. As discussed above, the access terminal mayreceive these frames at different times.

As represented by block 804, the access terminal determines a timingdifference between frames received from a first one of the access points(e.g., a serving femto cell) and at least one other one of the accesspoints (e.g., a macro cell). This may involve, for example, determiningthe parameter SFN-CFN OTD as discussed above.

As represented by block 806, the access terminal sends the timingdifference information to the first access point. For example, theaccess terminal may send the parameter SFN-CFN OTD via an MRM asdiscussed herein. The first access point receives this timing differenceinformation as represented by block 808.

As represented by block 810, the first access point determines itstiming error based on the received timing difference information. Thismay involve, for example, calculating or estimating the parameter Tm.Here, it should be appreciated that the access point may readily removethe parameter OFF×38400 from the parameter SFN-CFN OTD since this is amultiple of the number of chips in a frame.

As represented by block 812, the first access point adjusts a clock usedfor transmitting signals based on the determined timing error. Forexample, the first access point may adjust the phase of the clock basedon a single timing error value or based on several timing error valuesreceived from the access terminal over a period of time (e.g., bycalculating an average of the timing error values over a certainduration). Also, as discussed in more detail below, the first accesspoint may adjust the frequency of the clock based on the rate of changeof timing error values received from the access terminal over a periodof time.

Many of the procedures described herein in conjunction with otherfigures may apply to a received frame timing-based tracking scheme. Forexample, the accuracy of the estimated time and/or frequency error maybe improved by requesting the access terminal to send periodic MRMs.

As mentioned above, using OTD reports for frequency and time tracking isapplicable when the access terminal is in CELL_DCH, IDLE mode or anyother state for which OTD is supported. In the idle mode, one potentialissue is that the femto cell may not know when the access terminalleaves the femto cell (e.g., reselects to a macro cell). However, thefemto cell may request periodic location updates from the accessterminal or change the femto cell location area code (LAC) to be able todetect whether the access terminal is still there or not.

FIG. 9 illustrates sample operations that may be performed to providefrequency tracking as taught herein. Frequency drift of a femto celltranslates into timing drift of the timing information received from anaccess terminal (e.g., timing (phase) drift of measured macro pilots ortiming drift of measured OTDs). By collecting timing information overtime (e.g., several macro PN phase measurements or several OTDmeasurements), this time drift and therefore the femto cell's frequencydrift may be estimated. For example, a femto cell may request periodicreports (e.g., PSMMs or MRMs) from an access terminal, divide thereceived measurements into different time intervals, estimate frequencydrift over each interval using linear regression, and select the averageor the median of these estimates as the frequency drift to be corrected.

As represented by block 902, to obtain reports over a period of time,the access point may need to send a message that requests the accessterminal to send timing information reports on a repeated basis (e.g.periodically). As represented by block 904, the access point receivestiming information reports from the access terminal on a repeated basis(e.g., once every few seconds) and then stores information from thereports. For example, the access point may store the parameter D, theparameter (e), the parameter SFN-CFN OTD, or the parameter Tm. Asrepresented by block 906, the access point determines the rate of changeof the timing information over a period of time. For example, the accesspoint may determine the rate of change of the parameter (e) or theparameter Tm. As represented by blocks 908 and 910, the access pointthen determines a frequency adjustment based on the determined rate ofchange and adjusts the clock based on the determined frequencyadjustment.

Referring now to FIGS. 10 and 11, an access point may acquire timinginformation from a variety of timing sources. For example, a femto cellmay request an access terminal to report timing information frommultiple timing sources (e.g., request the access terminal to measureand report phase difference between its own pilot and multiple macropilots, or measure and report OTDs with respect to multiple macro accesspoints), after which the femto cell jointly uses the timing informationfrom these macro access points for tracking purpose. In addition, afemto cell may request multiple access terminals to each report timinginformation (e.g., request each access terminal to measure and report atleast one macro pilot, or measure and report OTDs with respect to atleast one macro access point), after which the femto cell jointly usesthe timing information received from these access terminals (e.g. viaPSMMs, CFSRPMs, or MRMs) for tracking purpose. Here, a given one ofthese access terminals may be idling on or in an active call with thefemto cell.

As mentioned above, the teachings herein may be employed in varioustechnologies. For example, the described techniques may be used incdma2000 1×RTT, UMTS, WiMax, LTE, GSM, and other technologies. Inaddition, an access point may perform time and/or frequency trackingbased on timing information associated with one or more technologies.For example, an access point may acquire timing information from acdma2000 timing source and a UMTS source, and adjust its clock based ona combination (e.g., weighted combination) of this timing information.This multi-technology timing information may be obtained, for example,via an access terminal that supports multiple technologies. As anotherexample, this multi-technology timing information may be obtained viadifferent access terminals that each support a different technology in acase where the access point supports communicating with different accessterminals via different technologies.

FIG. 10 illustrates sample operations where an access point requests atleast one access terminal to report timing information associated withat least one timing source. For example, in some cases, the access pointmay send a request to one access terminal to report timing informationfor one timing source. In some cases, the access point may send arequest to one access terminal to report timing information for multipletiming sources. In some cases, the access point may send requests tomultiple access terminals to report timing information for one timingsource. In some cases, the access point may send requests to multipleaccess terminals to report timing information for multiple timingsources (e.g., where the same or different timing sources may bespecified for different access terminals).

As represented by block 1002, the access point sends a message to eachaccess terminal, whereby the message causes the access terminal toreport timing information associated with at least one timing source.For example, a femto cell may send a message that explicitly requests anaccess terminal to determine and report timing differences between thefemto cell and several other cells. As discussed herein, in some cases,such a request may specify, for example, particular access points,cells, pilot PN codes, or frequencies from which the timing informationis to be acquired.

As represented by block 1004, each access terminal generates timinginformation associated with its corresponding timing source(s) asdiscussed herein. For example, the access terminal may receive signalsfrom the different timing sources using the appropriate radio technologyfor each timing source, if applicable. Then, for each timing source, theaccess terminal determines the timing difference between the accesspoint (e.g., the femto cell) and the timing source (e.g., a macro accesspoint).

As represented by block 1006, each access terminal sends its timinginformation to the access point. This information may be sent via asingle message or multiple messages.

As represented by block 1008, the access point receives the timinginformation sent by each access terminal. Accordingly, the access pointmay acquire different timing information associated with differenttiming sources. In addition, or alternatively, the access point mayacquire different timing information from different access terminals.

As represented by block 1010, in some implementations, the access pointmay weight the timing information. For example, a femto cell may apply aweighting factor to the timing information associated with a giventiming source based on the reliability of that timing source (e.g.,where the reliability may be determined from the perspective of theaccess terminal that provided the timing information). An example ofsuch a weighting scheme is described in more detail below in conjunctionwith FIG. 14.

As represented by block 1012, the access point adjusts its clock basedon the received timing information. As discussed herein, this timinginformation may have been received from different access terminalsand/or may be associated with different timing sources. Thus, theweighting may be applied based on the different access terminals thatprovided the timing information and/or the different timing sources. Forexample, the access point may determine the average of a set of weightedtiming error values associated with the different timing sources and usethe resulting average to adjust the clock. Alternatively, the accesspoint may determine the worst case (e.g., highest) value of a set ofweighted timing error values associated with the different timingsources and use that worst case value to adjust the clock. As anotherexample, the access point may determine the average of a set of weightedtiming error values associated with the different access terminals anduse the resulting average to adjust the clock. Alternatively, the accesspoint may determine the worst case (e.g., highest) value of a set ofweighted timing error values associated with the different accessterminals and use that worst case value to adjust the clock.

Referring now to FIG. 11, the accuracy of the estimated time and/orfrequency error may be improved by requesting an access terminal torepeatedly send timing information (e.g., send periodic PSMMs or MRMs).The rate at which the timing information is sent may be set by a femtocell by estimating the reliability of the femto cell's current time andfrequency accuracy, and estimating how frequently macro measurementswill be needed before time and frequency error become unacceptable.

Accordingly, as represented by block 1102, the access point estimatesthe reliability of its clock (e.g., on a repeated basis). This mayinvolve, for example, keeping track of the magnitude of the timing erroradjustments that are made for the clock.

As represented by block 1104, the access point determines the rate atwhich timing information should be provided by the access terminal basedon the estimated reliability of the clock. For example, if themagnitudes of the timing error adjustments are relatively large, it maybe necessary to receive timing information at a higher (faster) rate toensure that the clock is adjusted frequently enough so that the accesspoint continues to meet system timing requirements. Conversely, if themagnitudes of the timing error adjustments are relatively small, thetiming information may be received at a lower (slower) rate.

As represented by block 1106, the access point sends a message to theaccess terminal that requests the access terminal to send timinginformation at the rate determined at block 1104. Accordingly, theaccess point will receive timing information from the access terminal atthe requested rate as represented by block 1108.

As represented by block 1110, the access point adjusts its clock basedon the received timing information as discussed herein. The access pointmay repeat the operations of blocks 1102-1106 to update the requestedrate, as needed, based on the currently reliability of the clock.

FIG. 12 describes sample operations that an access point may perform todetermine whether to use timing information from a timing source. Inparticular, this decision may be based on the accuracy of the timingsource (e.g., whether the timing source is GPS-based).

As represented by block 1202, at some point in time, the access pointreceives information indicative of the accuracy of one or more timingsources. For example, a femto cell may determine that certain PN offsetsare used by access points (e.g., macro access points) that use a highlyaccurate timing source. Alternatively, the femto cell may receive amessage (e.g., an overhead message) that indicates that a given accesspoint has an accurate timing source. In some cases, the access pointreceives this type of information from the network (e.g., from aconfiguration server) via the backhaul. In some cases, the access pointmay learn this type of information (e.g., by analyzing received timinginformation).

As represented by block 1204, at some point in time, the access pointreceives timing information associated with at least one timing sourcefrom at least one access terminal (e.g., as discussed herein). Forexample, a femto cell may receive the parameter D or the parameterSFN-CFN OTD as discussed above.

As represented by block 1206, for each timing source, the access pointdetermines whether that timing source has sufficiently accurate timing.For example, a femto cell may determine that a reported PN phase belongsto a macro access point by mapping the reported phase to a PN Offset andverifying that this PN Offset belongs to a macro access point (e.g.,that uses GPS-based timing).

As represented by block 1208, the access point determines whether to usethe timing information associated with a given timing source based onwhether that timing source has sufficiently accurate timing. Forexample, if the timing source is sufficiently accurate, the femto cellmay elect to use the associated timing information to adjust its clockat block 1210.

FIG. 13 illustrates sample operations that may be performed for animplementation where timing information from different timing sourcesare weighted based on the reliability of the timing sources.

As represented by block 1302, the access point receives timinginformation associated with several timing sources from at least oneaccess terminal (e.g., as discussed herein). For example, a femto cellmay receive the parameter D or the parameter SFN-CFN OTD as discussedabove for each timing source.

As represented by block 1304, the access point determines thereliability of each timing source. For example, the access terminal thatreported the timing information for that timing source also may reportthe received signal strength of the signal (e.g., pilot channel signal,common channel signal, or dedicated channel signal) from which theaccess acquired the timing information. Accordingly, the femto cell mayrank the reliability of a given timing source based on the correspondingreceived signal strength.

As represented by block 1306, the access point then weights the timinginformation associated with a given timing source based on thedetermined reliability of that timing source. For example, a femto cellmay apply a weighting factor to the timing information received from agiven access terminal based on the magnitude of the correspondingreceived signal strength (e.g., a higher received signal strengthcorresponds to a higher weight).

As represented by block 1308, the access point adjusts its clock basedon the weighted timing information. For example, the access point maydetermine the average of a set of weighted timing error valuesassociated with the different timing sources and use the resultingaverage to adjust the clock. Alternatively, the access point maydetermine the worst case (e.g., highest) value of a set of weightedtiming error values associated with the different timing sources and usethat worst case value to adjust the clock.

Other techniques may be employed in accordance with the teachings hereinto generate an error correction value that is used to adjust a clock.For example, an access point may filter the reports (e.g., PSMMs orMRMs) it receives over a period of time (e.g., a few minutes). Theaccess point may remove any reports with a reported macro Ecp/Io that isless that a specified threshold (e.g., −18 dB). The access point maythen compute a frequency error for each timing source (e.g., for eachreported macro primary scrambling code). Next, the access point maydetermine a weighted average of the frequency errors (e.g., where theweights are proportional to the number of reports received for the macrocell). The access point may then apply frequency error correction (e.g.,adjust the frequency of the clock) based on the determined weightedaverage.

FIG. 14 illustrates several sample components (represented bycorresponding blocks) that may be incorporated into nodes such as anaccess point 1402 (e.g., corresponding to the access point 104 ofFIG. 1) to perform timing control-related operations as taught herein.The described components also may be incorporated into other nodes in acommunication system. For example, other nodes in a system may includecomponents similar to those described for the access point 1402 toprovide similar functionality. Also, a given node may contain one ormore of the described components. For example, an access point maycontain multiple transceiver components that enable the access point tooperate on multiple carriers and/or communicate via differenttechnologies.

As shown in FIG. 14, the access point 1402 includes a transceiver 1404for communicating with other nodes (e.g., access terminals). Thetransceiver 1404 includes a transmitter 1406 for sending signals (e.g.,pilot signals, frames, messages, requests) and a receiver 1408 forreceiving signals (e.g., messages, responses, timing information).

The access point 1402 also includes a network interface 1410 forcommunicating with other nodes (e.g., network entities). For example,the network interface 1410 may be configured to communicate with one ormore network entities via a wire-based or wireless backhaul. In someaspects, the network interface 1410 may be implemented as a transceiver(e.g., including transmitter and receiver components) configured tosupport wire-based or wireless communication. Accordingly, in theexample of FIG. 14, the network interface 1410 is shown as including atransmitter 1412 and a receiver 1414.

The access point 1402 includes other components that may be used inconjunction with timing control-related operations as taught herein. Forexample, the access point 1402 includes a mode controller 1416 (e.g.,corresponding to the component 122 of FIG. 1) for detecting a mode ofoperation of the access point 1402 and/or of nearby access terminals(e.g., determining that an access point is handing an active call,determining that an access terminal is in idle mode) and for providingother related functionality as taught herein. In some implementations,some of the functionality of the mode controller 1416 may be implementedin the transceiver 1404. The access point 1402 also includes a timingcontroller 1418 (e.g., corresponding to the component 124 of FIG. 1) forcontrolling timing at the access point 1402 (e.g., acquiring timinginformation, adjusting a clock, estimating the reliability of a clock,determining a rate at which timing information should be provided,acquiring other timing information, determining that an access point hassufficiently accurate timing, electing to use timing information,acquiring timing information associated with at least one other timingsource, determining reliability of a timing source, weighting timinginformation) and for providing other related functionality as taughtherein. In addition, the access point 1402 includes a communicationcontroller 1420 for facilitating communications by the access point 1402(e.g., sending at least one request, sending a message, receiving amessage, receiving a response) and for providing other relatedfunctionality as taught herein. In some implementations, some of thefunctionality of the communication controller 1420 may be implemented inthe transceiver 1404 and/or the network interface 1410. Also, the accesspoint 1402 includes a memory component 1422 (e.g., including a memorydevice) for maintaining information (e.g., timing information, timingsource search information, report information, and so on).

For convenience, the access point 1402 is shown in FIG. 14 as includingcomponents that may be used in the various examples described herein. Inpractice, the functionality of one or more of these blocks may bedifferent in different embodiments. For example, the functionality ofblock 1416 may be different in an embodiment implemented in accordancewith FIG. 2 as compared to an embodiment implemented in accordance withFIG. 3.

The components of FIG. 14 may be implemented in various ways. In someimplementations the components of FIG. 14 may be implemented in one ormore circuits such as, for example, one or more processors and/or one ormore ASICs (which may include one or more processors). Here, eachcircuit (e.g., processor) may use and/or incorporate data memory forstoring information or executable code used by the circuit to providethis functionality. For example, some of the functionality representedby blocks 1404 and 1410, and some or all of the functionalityrepresented by blocks 1416-1422 may be implemented by a processor orprocessors of an access point and data memory of the access point (e.g.,by execution of appropriate code and/or by appropriate configuration ofprocessor components).

As discussed above, the teachings herein may be employed in a networkthat includes macro scale coverage (e.g., a large area cellular networksuch as a 3G network, typically referred to as a macro cell network or aWAN) and smaller scale coverage (e.g., a residence-based orbuilding-based network environment, typically referred to as a LAN). Asan access terminal (AT) moves through such a network, the accessterminal may be served in certain locations by access points thatprovide macro coverage while the access terminal may be served at otherlocations by access points that provide smaller scale coverage. In someaspects, the smaller coverage nodes may be used to provide incrementalcapacity growth, in-building coverage, and different services (e.g., fora more robust user experience).

In the description herein, a node (e.g., an access point) that providescoverage over a relatively large area may be referred to as a macroaccess point while a node that provides coverage over a relatively smallarea (e.g., a residence) may be referred to as a femto access point. Itshould be appreciated that the teachings herein may be applicable tonodes associated with other types of coverage areas. For example, a picoaccess point may provide coverage (e.g., coverage within a commercialbuilding) over an area that is smaller than a macro area and larger thana femto area. In various applications, other terminology may be used toreference a macro access point, a femto access point, or other accesspoint-type nodes. For example, a macro access point may be configured orreferred to as an access node, base station, access point, eNodeB, macrocell, and so on. Also, a femto access point may be configured orreferred to as a Home NodeB, Home eNodeB, access point base station,femto cell, and so on. In some implementations, a node may be associatedwith (e.g., referred to as or divided into) one or more cells orsectors. A cell or sector associated with a macro access point, a femtoaccess point, or a pico access point may be referred to as a macro cell,a femto cell, or a pico cell, respectively.

FIG. 15 illustrates a wireless communication system 1500, configured tosupport a number of users, in which the teachings herein may beimplemented. The system 1500 provides communication for multiple cells1502, such as, for example, macro cells 1502A-1502G, with each cellbeing serviced by a corresponding access point 1504 (e.g., access points1504A-1504G). As shown in FIG. 15, access terminals 1506 (e.g., accessterminals 1506A-1506L) may be dispersed at various locations throughoutthe system over time. Each access terminal 1506 may communicate with oneor more access points 1504 on a forward link (FL) and/or a reverse link(RL) at a given moment, depending upon whether the access terminal 1506is active and whether it is in soft handoff, for example. The wirelesscommunication system 1500 may provide service over a large geographicregion. For example, macro cells 1502A-1502G may cover a few blocks in aneighborhood or several miles in a rural environment.

FIG. 16 illustrates an exemplary communication system 1600 where one ormore femto access points are deployed within a network environment.Specifically, the system 1600 includes multiple femto access points 1610(e.g., femto access points 1610A and 1610B) installed in a relativelysmall scale network environment (e.g., in one or more user residences1630). Each femto access point 1610 may be coupled to a wide areanetwork 1640 (e.g., the Internet) and a mobile operator core network1650 via a DSL router, a cable modem, a wireless link, or otherconnectivity means (not shown). As will be discussed below, each femtoaccess point 1610 may be configured to serve associated access terminals1620 (e.g., access terminal 1620A) and, optionally, other (e.g., hybridor alien) access terminals 1620 (e.g., access terminal 1620B). In otherwords, access to femto access points 1610 may be restricted whereby agiven access terminal 1620 may be served by a set of designated (e.g.,home) femto access point(s) 1610 but may not be served by anynon-designated femto access points 1610 (e.g., a neighbor's femto accesspoint 1610).

FIG. 17 illustrates an example of a coverage map 1700 where severaltracking areas 1702 (or routing areas or location areas) are defined,each of which includes several macro coverage areas 1704. Here, areas ofcoverage associated with tracking areas 1702A, 1702B, and 1702C aredelineated by the wide lines and the macro coverage areas 1704 arerepresented by the larger hexagons. The tracking areas 1702 also includefemto coverage areas 1706. In this example, each of the femto coverageareas 1706 (e.g., femto coverage areas 1706B and 1706C) is depictedwithin one or more macro coverage areas 1704 (e.g., macro coverage areas1704A and 1704B). It should be appreciated, however, that some or all ofa femto coverage area 1706 may not lie within a macro coverage area1704. In practice, a large number of femto coverage areas 1706 (e.g.,femto coverage areas 1706A and 1706D) may be defined within a giventracking area 1702 or macro coverage area 1704. Also, one or more picocoverage areas (not shown) may be defined within a given tracking area1702 or macro coverage area 1704.

Referring again to FIG. 16, the owner of a femto access point 1610 maysubscribe to mobile service, such as, for example, 3G mobile service,offered through the mobile operator core network 1650. In addition, anaccess terminal 1620 may be capable of operating both in macroenvironments and in smaller scale (e.g., residential) networkenvironments. In other words, depending on the current location of theaccess terminal 1620, the access terminal 1620 may be served by a macrocell access point 1660 associated with the mobile operator core network1650 or by any one of a set of femto access points 1610 (e.g., the femtoaccess points 1610A and 1610B that reside within a corresponding userresidence 1630). For example, when a subscriber is outside his home, heis served by a standard macro access point (e.g., access point 1660) andwhen the subscriber is at home, he is served by a femto access point(e.g., access point 1610A). Here, a femto access point 1610 may bebackward compatible with legacy access terminals 1620.

A femto access point 1610 may be deployed on a single frequency or, inthe alternative, on multiple frequencies. Depending on the particularconfiguration, the single frequency or one or more of the multiplefrequencies may overlap with one or more frequencies used by a macroaccess point (e.g., access point 1660).

In some aspects, an access terminal 1620 may be configured to connect toa preferred femto access point (e.g., the home femto access point of theaccess terminal 1620) whenever such connectivity is possible. Forexample, whenever the access terminal 1620A is within the user'sresidence 1630, it may be desired that the access terminal 1620Acommunicate only with the home femto access point 1610A or 1610B.

In some aspects, if the access terminal 1620 operates within the macrocellular network 1650 but is not residing on its most preferred network(e.g., as defined in a preferred roaming list), the access terminal 1620may continue to search for the most preferred network (e.g., thepreferred femto access point 1610) using a better system reselection(BSR) procedure, which may involve a periodic scanning of availablesystems to determine whether better systems are currently available andsubsequently acquire such preferred systems. The access terminal 1620may limit the search for specific band and channel. For example, one ormore femto channels may be defined whereby all femto access points (orall restricted femto access points) in a region operate on the femtochannel(s). The search for the most preferred system may be repeatedperiodically. Upon discovery of a preferred femto access point 1610, theaccess terminal 1620 selects the femto access point 1610 and registerson it for use when within its coverage area.

Access to a femto access point may be restricted in some aspects. Forexample, a given femto access point may only provide certain services tocertain access terminals. In deployments with so-called restricted (orclosed) access, a given access terminal may only be served by the macrocell mobile network and a defined set of femto access points (e.g., thefemto access points 1610 that reside within the corresponding userresidence 1630). In some implementations, an access point may berestricted to not provide, for at least one node (e.g., accessterminal), at least one of: signaling, data access, registration,paging, or service.

In some aspects, a restricted femto access point (which may also bereferred to as a Closed Subscriber Group Home NodeB) is one thatprovides service to a restricted provisioned set of access terminals.This set may be temporarily or permanently extended as necessary. Insome aspects, a Closed Subscriber Group (CSG) may be defined as the setof access points (e.g., femto access points) that share a common accesscontrol list of access terminals.

Various relationships may thus exist between a given femto access pointand a given access terminal. For example, from the perspective of anaccess terminal, an open femto access point may refer to a femto accesspoint with unrestricted access (e.g., the femto access point allowsaccess to any access terminal). A restricted femto access point mayrefer to a femto access point that is restricted in some manner (e.g.,restricted for access and/or registration). A home femto access pointmay refer to a femto access point on which the access terminal isauthorized to access and operate on (e.g., permanent access is providedfor a defined set of one or more access terminals). A hybrid (or guest)femto access point may refer to a femto access point on which differentaccess terminals are provided different levels of service (e.g., someaccess terminals may be allowed partial and/or temporary access whileother access terminals may be allowed full access). An alien femtoaccess point may refer to a femto access point on which the accessterminal is not authorized to access or operate on, except for perhapsemergency situations (e.g., 911 calls).

From a restricted femto access point perspective, a home access terminalmay refer to an access terminal that is authorized to access therestricted femto access point installed in the residence of that accessterminal's owner (usually the home access terminal has permanent accessto that femto access point). A guest access terminal may refer to anaccess terminal with temporary access to the restricted femto accesspoint (e.g., limited based on deadline, time of use, bytes, connectioncount, or some other criterion or criteria). An alien access terminalmay refer to an access terminal that does not have permission to accessthe restricted femto access point, except for perhaps emergencysituations, for example, such as 911 calls (e.g., an access terminalthat does not have the credentials or permission to register with therestricted femto access point).

For convenience, the disclosure herein describes various functionalityin the context of a femto access point. It should be appreciated,however, that a pico access point may provide the same or similarfunctionality for a larger coverage area. For example, a pico accesspoint may be restricted, a home pico access point may be defined for agiven access terminal, and so on.

The teachings herein may be employed in a wireless multiple-accesscommunication system that simultaneously supports communication formultiple wireless access terminals. Here, each terminal may communicatewith one or more access points via transmissions on the forward andreverse links. The forward link (or downlink) refers to thecommunication link from the access points to the terminals, and thereverse link (or uplink) refers to the communication link from theterminals to the access points. This communication link may beestablished via a single-in-single-out system, amultiple-in-multiple-out (MIMO) system, or some other type of system.

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(S) independent channels, which are also referred to as spatialchannels, where N_(S)≦min{N_(T), N_(R)}. Each of the N_(S) independentchannels corresponds to a dimension. The MIMO system may provideimproved performance (e.g., higher throughput and/or greaterreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

A MIMO system may support time division duplex (TDD) and frequencydivision duplex (FDD). In a TDD system, the forward and reverse linktransmissions are on the same frequency region so that the reciprocityprinciple allows the estimation of the forward link channel from thereverse link channel. This enables the access point to extract transmitbeam-forming gain on the forward link when multiple antennas areavailable at the access point.

FIG. 18 illustrates a wireless device 1810 (e.g., an access point) and awireless device 1850 (e.g., an access terminal) of a sample MIMO system1800. At the device 1810, traffic data for a number of data streams isprovided from a data source 1812 to a transmit (TX) data processor 1814.Each data stream may then be transmitted over a respective transmitantenna.

The TX data processor 1814 formats, codes, and interleaves the trafficdata for each data stream based on a particular coding scheme selectedfor that data stream to provide coded data. The coded data for each datastream may be multiplexed with pilot data using OFDM techniques. Thepilot data is typically a known data pattern that is processed in aknown manner and may be used at the receiver system to estimate thechannel response. The multiplexed pilot and coded data for each datastream is then modulated (i.e., symbol mapped) based on a particularmodulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM) selected for thatdata stream to provide modulation symbols. The data rate, coding, andmodulation for each data stream may be determined by instructionsperformed by a processor 1830. A data memory 1832 may store programcode, data, and other information used by the processor 1830 or othercomponents of the device 1810.

The modulation symbols for all data streams are then provided to a TXMIMO processor 1820, which may further process the modulation symbols(e.g., for OFDM). The TX MIMO processor 1820 then provides N_(T)modulation symbol streams to N_(T) transceivers (XCVR) 1822A through1822T. In some aspects, the TX MIMO processor 1820 applies beam-formingweights to the symbols of the data streams and to the antenna from whichthe symbol is being transmitted.

Each transceiver 1822 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transceivers 1822A through 1822T are thentransmitted from N_(T) antennas 1824A through 1824T, respectively.

At the device 1850, the transmitted modulated signals are received byN_(R) antennas 1852A through 1852R and the received signal from eachantenna 1852 is provided to a respective transceiver (XCVR) 1854Athrough 1854R. Each transceiver 1854 conditions (e.g., filters,amplifies, and downconverts) a respective received signal, digitizes theconditioned signal to provide samples, and further processes the samplesto provide a corresponding “received” symbol stream.

A receive (RX) data processor 1860 then receives and processes the N_(R)received symbol streams from N_(R) transceivers 1854 based on aparticular receiver processing technique to provide N_(T) “detected”symbol streams. The RX data processor 1860 then demodulates,deinterleaves, and decodes each detected symbol stream to recover thetraffic data for the data stream. The processing by the RX dataprocessor 1860 is complementary to that performed by the TX MIMOprocessor 1820 and the TX data processor 1814 at the device 1810.

A processor 1870 periodically determines which pre-coding matrix to use(discussed below). The processor 1870 formulates a reverse link messagecomprising a matrix index portion and a rank value portion. A datamemory 1872 may store program code, data, and other information used bythe processor 1870 or other components of the device 1850.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 1838,which also receives traffic data for a number of data streams from adata source 1836, modulated by a modulator 1880, conditioned by thetransceivers 1854A through 1854R, and transmitted back to the device1810.

At the device 1810, the modulated signals from the device 1850 arereceived by the antennas 1824, conditioned by the transceivers 1822,demodulated by a demodulator (DEMOD) 1840, and processed by a RX dataprocessor 1842 to extract the reverse link message transmitted by thedevice 1850. The processor 1830 then determines which pre-coding matrixto use for determining the beam-forming weights then processes theextracted message.

FIG. 18 also illustrates that the communication components may includeone or more components that perform timing control operations as taughtherein. For example, a timing control component 1890 may cooperate withthe processor 1830 and/or other components of the device 1810 to adjusta clock that may be used for sending/receiving signals to/from anotherdevice (e.g., device 1850) as taught herein. It should be appreciatedthat for each device 1810 and 1850 the functionality of two or more ofthe described components may be provided by a single component. Forexample, a single processing component may provide the functionality ofthe timing control component 1890 and the processor 1830.

The teachings herein may be incorporated into various types ofcommunication systems and/or system components. In some aspects, theteachings herein may be employed in a multiple-access system capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., by specifying one or more of bandwidth, transmitpower, coding, interleaving, and so on). For example, the teachingsherein may be applied to any one or combinations of the followingtechnologies: Code Division Multiple Access (CDMA) systems,Multiple-Carrier CDMA (MCCDMA), Wideband CDMA (W-CDMA), High-SpeedPacket Access (HSPA, HSPA+) systems, Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems,Single-Carrier FDMA (SC-FDMA) systems, Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, or other multiple access techniques. Awireless communication system employing the teachings herein may bedesigned to implement one or more standards, such as IS-95, cdma2000,IS-856, W-CDMA, TDSCDMA, and other standards. A CDMA network mayimplement a radio technology such as Universal Terrestrial Radio Access(UTRA), cdma2000, or some other technology. UTRA includes W-CDMA and LowChip Rate (LCR). The cdma2000 technology covers IS-2000, IS-95 andIS-856 standards. A TDMA network may implement a radio technology suchas Global System for Mobile Communications (GSM). An OFDMA network mayimplement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11,IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM arepart of Universal Mobile Telecommunication System (UMTS). The teachingsherein may be implemented in a 3GPP Long Term Evolution (LTE) system, anUltra-Mobile Broadband (UMB) system, and other types of systems. LTE isa release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE aredescribed in documents from an organization named “3rd GenerationPartnership Project” (3GPP), while cdma2000 is described in documentsfrom an organization named “3rd Generation Partnership Project 2”(3GPP2). Although certain aspects of the disclosure may be describedusing 3GPP terminology, it is to be understood that the teachings hereinmay be applied to 3GPP (e.g., Rel99, Rel5, Rel6, Rel7, etc.) technology,as well as 3GPP2 (e.g., 1×RTT, 1×EV-DO Rel0, RevA, RevB) technology andother technologies.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of apparatuses (e.g., nodes). In someaspects, a node (e.g., a wireless node) implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

For example, an access terminal may comprise, be implemented as, orknown as user equipment, a subscriber station, a subscriber unit, amobile station, a mobile, a mobile node, a remote station, a remoteterminal, a user terminal, a user agent, a user device, or some otherterminology. In some implementations an access terminal may comprise acellular telephone, a cordless telephone, a session initiation protocol(SIP) phone, a wireless local loop (WLL) station, a personal digitalassistant (PDA), a handheld device having wireless connectioncapability, or some other suitable processing device connected to awireless modem. Accordingly, one or more aspects taught herein may beincorporated into a phone (e.g., a cellular phone or smart phone), acomputer (e.g., a laptop), a portable communication device, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music device, a video device, or a satellite radio), aglobal positioning system device, or any other suitable device that isconfigured to communicate via a wireless medium.

An access point may comprise, be implemented as, or known as a NodeB, aneNodeB, a radio network controller (RNC), a base station (BS), a radiobase station (RBS), a base station controller (BSC), a base transceiverstation (BTS), a transceiver function (TF), a radio transceiver, a radiorouter, a basic service set (BSS), an extended service set (ESS), amacro cell, a macro node, a Home eNB (HeNB), a femto cell, a femto node,a pico node, or some other similar terminology.

In some aspects a node (e.g., an access point) may comprise an accessnode for a communication system. Such an access node may provide, forexample, connectivity for or to a network (e.g., a wide area networksuch as the Internet or a cellular network) via a wired or wirelesscommunication link to the network. Accordingly, an access node mayenable another node (e.g., an access terminal) to access a network orsome other functionality. In addition, it should be appreciated that oneor both of the nodes may be portable or, in some cases, relativelynon-portable.

Also, it should be appreciated that a wireless node may be capable oftransmitting and/or receiving information in a non-wireless manner(e.g., via a wired connection). Thus, a receiver and a transmitter asdiscussed herein may include appropriate communication interfacecomponents (e.g., electrical or optical interface components) tocommunicate via a non-wireless medium.

A wireless node may communicate via one or more wireless communicationlinks that are based on or otherwise support any suitable wirelesscommunication technology. For example, in some aspects a wireless nodemay associate with a network. In some aspects the network may comprise alocal area network or a wide area network. A wireless device may supportor otherwise use one or more of a variety of wireless communicationtechnologies, protocols, or standards such as those discussed herein(e.g., CDMA, TDMA, OFDM, OFDMA, WiMAX, Wi-Fi, and so on). Similarly, awireless node may support or otherwise use one or more of a variety ofcorresponding modulation or multiplexing schemes. A wireless node maythus include appropriate components (e.g., air interfaces) to establishand communicate via one or more wireless communication links using theabove or other wireless communication technologies. For example, awireless node may comprise a wireless transceiver with associatedtransmitter and receiver components that may include various components(e.g., signal generators and signal processors) that facilitatecommunication over a wireless medium.

The functionality described herein (e.g., with regard to one or more ofthe accompanying figures) may correspond in some aspects to similarlydesignated “means for” functionality in the appended claims. Referringto FIGS. 19-21, apparatuses 1900 and 2100 are represented as a series ofinterrelated functional modules. Here, a module for determining that anaccess point is handing an active call 1902 may correspond at least insome aspects to, for example, a mode controller as discussed herein. Amodule for acquiring timing information 1904 may correspond at least insome aspects to, for example, a timing controller as discussed herein. Amodule for adjusting a clock 1906 may correspond at least in someaspects to, for example, a timing controller as discussed herein. Amodule for estimating the reliability of a clock 1908 may correspond atleast in some aspects to, for example, a timing controller as discussedherein. A module for determining a rate at which timing informationshould be provided 1910 may correspond at least in some aspects to, forexample, a timing controller as discussed herein. A module for acquiringother timing information 1912 may correspond at least in some aspectsto, for example, a timing controller as discussed herein. A module forsending at least one request 1914 may correspond at least in someaspects to, for example, a communication controller as discussed herein.A module for determining that an access point has sufficiently accuratetiming 1916 may correspond at least in some aspects to, for example, atiming controller as discussed herein. A module for electing to usetiming information 1918 may correspond at least in some aspects to, forexample, a timing controller as discussed herein. A module for acquiringtiming information associated with at least one other timing source 1920may correspond at least in some aspects to, for example, a timingcontroller as discussed herein. A module for determining reliability ofa timing source 1922 may correspond at least in some aspects to, forexample, a timing controller as discussed herein. A module for weightingtiming information 1924 may correspond at least in some aspects to, forexample, a timing controller as discussed herein. A module fordetermining that an access terminal is in idle mode 1926 may correspondat least in some aspects to, for example, a mode controller as discussedherein. A module for sending a message 1928 may correspond at least insome aspects to, for example, a communication controller as discussedherein. A module for determining that an access terminal is in idle mode2102 may correspond at least in some aspects to, for example, a timingcontroller as discussed herein. A module for acquiring timinginformation 2104 may correspond at least in some aspects to, forexample, a timing controller as discussed herein. A module for adjustinga clock 2106 may correspond at least in some aspects to, for example, atiming controller as discussed herein. A module for estimating thereliability of a clock 2108 may correspond at least in some aspects to,for example, a timing controller as discussed herein. A module fordetermining a rate at which timing information should be provided 2110may correspond at least in some aspects to, for example, a timingcontroller as discussed herein. A module for determining that an accesspoint has sufficiently accurate timing 2112 may correspond at least insome aspects to, for example, a timing controller as discussed herein. Amodule for electing to use timing information 2114 may correspond atleast in some aspects to, for example, a timing controller as discussedherein.

The functionality of the modules of FIGS. 19-21 may be implemented invarious ways consistent with the teachings herein. In some aspects thefunctionality of these modules may be implemented as one or moreelectrical components. In some aspects the functionality of these blocksmay be implemented as a processing system including one or moreprocessor components. In some aspects the functionality of these modulesmay be implemented using, for example, at least a portion of one or moreintegrated circuits (e.g., an ASIC). As discussed herein, an integratedcircuit may include a processor, software, other related components, orsome combination thereof. The functionality of these modules also may beimplemented in some other manner as taught herein. In some aspects oneor more of any dashed blocks in FIGS. 19-21 are optional.

It should be understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not generallylimit the quantity or order of those elements. Rather, thesedesignations may be used herein as a convenient method of distinguishingbetween two or more elements or instances of an element. Thus, areference to first and second elements does not mean that only twoelements may be employed there or that the first element must precedethe second element in some manner. Also, unless stated otherwise a setof elements may comprise one or more elements. In addition, terminologyof the form “at least one of: A, B, or C” used in the description or theclaims means “A or B or C or any combination of these elements.”

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that any of the variousillustrative logical blocks, modules, processors, means, circuits, andalgorithm steps described in connection with the aspects disclosedherein may be implemented as electronic hardware (e.g., a digitalimplementation, an analog implementation, or a combination of the two,which may be designed using source coding or some other technique),various forms of program or design code incorporating instructions(which may be referred to herein, for convenience, as “software” or a“software module”), or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implementedwithin or performed by an integrated circuit (IC), an access terminal,or an access point. The IC may comprise a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, electrical components, optical components,mechanical components, or any combination thereof designed to performthe functions described herein, and may execute codes or instructionsthat reside within the IC, outside of the IC, or both. A general purposeprocessor may be a microprocessor, but in the alternative, the processormay be any conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media. It should beappreciated that a computer-readable medium may be implemented in anysuitable computer-program product.

The previous description of the disclosed aspects is provided to enableany person skilled in the art to make or use the present disclosure.Various modifications to these aspects will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other aspects without departing from the scope of thedisclosure. Thus, the present disclosure is not intended to be limitedto the aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. A method of communication, comprising:determining, at a femto cell access point, that the femto cell accesspoint is communicating with an access terminal via an active call over adedicated channel between the femto cell access point and the accessterminal; acquiring, at the femto cell access point, timing informationfrom the access terminal during the communication as a result of thedetermining that the femto cell access point is communicating over thededicated channel; and adjusting, at the femto cell access point, aclock that controls transmissions by the femto cell access point,wherein the adjusting of the clock is based on the acquired timinginformation.
 2. The method of claim 1, wherein the timing information isindicative of a difference between timing associated with the femto cellaccess point and timing associated with at least one other cell.
 3. Themethod of claim 1, wherein the adjusting of the clock comprisesadjusting a phase of a signal transmitted by the femto cell access pointso that the adjusted phase is synchronized with a phase of transmissionof at least one other access point or with a phase of a timing source.4. The method of claim 1, wherein the adjusting of the clock comprisesadjusting a frequency of a signal transmitted by the femto cell accesspoint so that the adjusted frequency is synchronized with a transmitfrequency of at least one other access point or is matched to afrequency specified by network operation requirements.
 5. The method ofclaim 1, wherein: the timing information is indicative of timing ofanother access point or a timing source, which drives timing of an eventat the access terminal; and the adjusting of the clock comprisesadjusting timing of a signal transmission by the femto cell access pointso that the adjusted timing is synchronized with the timing of theevent.
 6. The method of claim 1, wherein the timing information isindicative of a phase difference between a first pilot signal receivedby the access terminal from the femto cell access point and a secondpilot signal received by the access terminal from another access point.7. The method of claim 1, wherein the acquiring of the timinginformation comprises receiving a pilot strength measurement messagefrom the access terminal, receiving a candidate frequency search reportfrom the access terminal, receiving a measurement report message fromthe access terminal, or receiving a route update message from the accessterminal.
 8. The method of claim 1, wherein the timing information isindicative of a timing difference between a time at which a frame fromthe femto cell access point is received by the access terminal and atime at which a frame from another access point is received by theaccess terminal.
 9. The method of claim 8, wherein the acquiring of thetiming information comprises receiving an observed time differencereport from the access terminal.
 10. The method of claim 1, wherein theacquiring of the timing information comprises sending a request to theaccess terminal for the timing information as a result of thedetermining that the femto cell access point is communicating over thededicated channel.
 11. The method of claim 10, wherein the acquiring ofthe timing information further comprises receiving a message includingthe timing information from the access terminal.
 12. The method of claim10, wherein the request for the timing information includes a list thatis indicative of at least one pilot signal for which the access terminalis to search to provide the timing information.
 13. The method of claim10, wherein the request for the timing information comprises a requestfor the access terminal to repeatedly provide timing informationreports.
 14. The method of claim 13, wherein: the timing informationreports are indicative of a plurality of timing differences between thefemto cell access point and another access point over a period of time;the adjusting of the clock comprises determining a rate of change of thetiming differences; the adjusting of the clock further comprisesdetermining a frequency adjustment based on the rate of change of thetiming differences; and the adjusting of the clock further comprisesadjusting a frequency of the clock based on the frequency adjustment.15. The method of claim 10, further comprising: estimating a reliabilityof the clock; and determining a rate at which the timing informationshould be provided by the access terminal based on the estimatedreliability, wherein the request for the timing information comprises arequest for the access terminal to provide the timing information at thedetermined rate.
 16. The method of claim 10, wherein the request for thetiming information comprises a request for the access terminal to searchfor signals on at least one specified carrier frequency.
 17. The methodof claim 10, wherein the request for the timing information comprises arequest for the access terminal to search for signals from a pluralityof other access points.
 18. The method of claim 17, wherein: the timinginformation is indicative of a plurality of timing differences betweenthe femto cell access point and at least a portion of the other accesspoints; and the adjusting of the clock is based on the plurality oftiming differences.
 19. The method of claim 10, further comprisingacquiring other timing information from at least one other accessterminal, wherein the adjusting of the clock is further based on theother timing information.
 20. The method of claim 19, wherein the timinginformation acquired from the access terminal is associated with a typeof radio technology and the other timing information acquired from theat least one other access terminal is associated with at least one othertype of radio technology.
 21. The method of claim 19, further comprisingsending at least one request to the at least one other access terminalto provide the other timing information.
 22. The method of claim 1,wherein the timing information is indicative of a timing differencebetween the femto cell access point and another access point, the methodfurther comprising: determining that the other access point hassufficiently accurate timing; and electing to use the timing informationreceived from the access terminal for the adjusting of the clock as aresult of the determining that the other access point has sufficientlyaccurate timing.
 23. The method of claim 1, wherein the timinginformation acquired from the access terminal is associated with a firsttiming source, the method further comprising: acquiring timinginformation associated with at least one other timing source; for eachtiming source, determining a reliability of the timing source; and foreach timing source, weighting the timing information associated with thetiming source based on the determined reliability of the timing source,wherein the adjusting of the clock is based on the weighted timinginformation.
 24. The method of claim 1, further comprising determiningthat the access terminal is in idle mode, wherein the timing informationis acquired from the access terminal as a result of the determining thatthe access terminal is in idle mode.
 25. The method of claim 24, whereinthe determining that the access terminal is in idle mode comprisesrequesting the access terminal to register with the femto cell accesspoint or requesting the access terminal to respond to a control channelmessage from the femto cell access point.
 26. The method of claim 24,wherein the acquiring of the timing information comprises sending amessage that requests the access terminal to send the timing informationto the femto cell access point.
 27. The method of claim 24, wherein theacquiring of the timing information comprises receiving a messageincluding the timing information from the access terminal.
 28. Themethod of claim 27, wherein the message comprises a radio environmentreport message or a route update message.
 29. The method of claim 1,wherein the timing information is indicative of a difference betweentiming associated with the femto cell access point and timing associatedwith a macro cell access point.
 30. An apparatus for communication,comprising: a mode controller configured to determine, at a femto cellaccess point, that the femto cell access point is communicating with anaccess terminal via an active call over a dedicated channel between thefemto cell access point and the access terminal; and a timing controllerconfigured to acquire, at the femto cell access point, timinginformation from the access terminal during the communication as aresult of the determining that the femto cell access point iscommunicating over the dedicated channel, and further configured toadjust, at the femto cell access point, a clock that controlstransmissions by the femto cell access point, wherein the adjusting ofthe clock is based on the acquired timing information.
 31. The apparatusof claim 30, wherein the timing information is indicative of adifference between timing associated with the femto cell access pointand timing associated with at least one other cell.
 32. The apparatus ofclaim 30, wherein the timing controller is configured to adjust theclock by adjusting a phase of a signal transmitted by the femto cellaccess point so that the adjusted phase is synchronized with a phase oftransmission of at least one other access point or with a phase of atiming source.
 33. The apparatus of claim 30, wherein the timingcontroller is configured to adjust the clock by adjusting a frequency ofa signal transmitted by the femto cell access point so that the adjustedfrequency is synchronized with a transmit frequency of at least oneother access point or is matched to a frequency specified by networkoperation requirements.
 34. The apparatus of claim 30, wherein thetiming information is indicative of a phase difference between a firstpilot signal received by the access terminal from the femto cell accesspoint and a second pilot signal received by the access terminal fromanother access point.
 35. The apparatus of claim 30, wherein the timinginformation is indicative of a timing difference between a time at whicha frame from the femto cell access point is received by the accessterminal and a time at which a frame from another access point isreceived by the access terminal.
 36. The apparatus of claim 30, whereinthe timing controller is configured to acquire the timing information bysending a request to the access terminal for the timing information as aresult of the determining that the femto cell access point iscommunicating over the dedicated channel.
 37. The apparatus of claim 36,wherein: the timing controller is further configured to estimate areliability of the clock; the timing controller is further configured todetermine a rate at which the timing information should be provided bythe access terminal based on the estimated reliability; and the requestfor the timing information comprises a request for the access terminalto provide the timing information at the determined rate.
 38. Theapparatus of claim 30, wherein: the timing information is indicative ofa timing difference between the femto cell access point and anotheraccess point; the timing controller is further configured to determinethat the other access point has sufficiently accurate timing; and thetiming controller is further configured to elect to use the timinginformation received from the access terminal for the adjusting of theclock as a result of the determining that the other access point hassufficiently accurate timing.
 39. The apparatus of claim 30, wherein:the mode controller is further configured to determine that the accessterminal is in idle mode; and the timing information is acquired fromthe access terminal as a result of the determining that the accessterminal is in idle mode.
 40. An apparatus for communication,comprising: means for determining, at a femto cell access point, thatthe femto cell access point is communicating with an access terminal viaan active call over a dedicated channel; means for acquiring, at thefemto cell access point, timing information from the access terminalduring the communication as a result of the determining that the femtocell access point is communicating over the dedicated channel betweenthe femto cell access point and the access terminal; and means foradjusting, at the femto cell access point, a clock that controlstransmissions by the femto cell access point, wherein the adjusting ofthe clock is based on the acquired timing information.
 41. The apparatusof claim 40, wherein the timing information is indicative of adifference between timing associated with the femto cell access pointand timing associated with at least one other cell.
 42. The apparatus ofclaim 40, wherein the means for adjusting the clock comprises means foradjusting a phase of a signal transmitted by the femto cell access pointso that the adjusted phase is synchronized with a phase of transmissionof at least one other access point or with a phase of a timing source.43. The apparatus of claim 40, wherein the means for adjusting the clockcomprises means for adjusting a frequency of a signal transmitted by thefemto cell access point so that the adjusted frequency is synchronizedwith a transmit frequency of at least one other access point or ismatched to a frequency specified by network operation requirements. 44.The apparatus of claim 40, wherein the timing information is indicativeof a phase difference between a first pilot signal received by theaccess terminal from the femto cell access point and a second pilotsignal received by the access terminal from another access point. 45.The apparatus of claim 40, wherein the timing information is indicativeof a timing difference between a time at which a frame from the femtocell access point is received by the access terminal and a time at whicha frame from another access point is received by the access terminal.46. The apparatus of claim 40, wherein the means for acquiring thetiming information comprises means for sending a request to the accessterminal for the timing information as a result of the determining thatthe femto cell access point is communicating over the dedicated channel.47. The apparatus of claim 46, further comprising: means for estimatinga reliability of the clock; and means for determining a rate at whichthe timing information should be provided by the access terminal basedon the estimated reliability, wherein the request for the timinginformation comprises a request for the access terminal to provide thetiming information at the determined rate.
 48. The apparatus of claim40, wherein the timing information is indicative of a timing differencebetween the femto cell access point and another access point, theapparatus further comprising: means for determining that the otheraccess point has sufficiently accurate timing; and means for electing touse the timing information received from the access terminal for theadjusting of the clock as a result of the determining that the otheraccess point has sufficiently accurate timing.
 49. The apparatus ofclaim 40, further comprising means for determining that the accessterminal is in idle mode, wherein the timing information is acquiredfrom the access terminal as a result of the determining that the accessterminal is in idle mode.
 50. A non-transitory computer-readable mediumcomprising code for causing a computer to: determine, at a femto cellaccess point, that the femto cell access point is communicating with anaccess terminal via an active call over a dedicated channel; acquire, atthe femto cell access point, timing information from the terminal duringthe communication as a result of the determining that the femto cellaccess point is communicating over the dedicated channel between thefemto cell access point and the access terminal; and adjust, at thefemto cell access point, a clock that controls transmissions by thefemto cell access point, wherein the adjusting of the clock is based onthe acquired timing information.
 51. The non-transitorycomputer-readable medium of claim 50, wherein the timing information isindicative of a difference between timing associated with the femto cellaccess point and timing associated with at least one other cell.
 52. Thenon-transitory computer-readable medium of claim 50, wherein theadjusting of the clock comprises adjusting a phase of a signaltransmitted by the femto cell access point so that the adjusted phase issynchronized with a phase of transmission of at least one other accesspoint or with a phase of a timing source.
 53. The non-transitorycomputer-readable medium of claim 50, wherein the adjusting of the clockcomprises adjusting a frequency of a signal transmitted by the femtocell access point so that the adjusted frequency is synchronized with atransmit frequency of at least one other access point or is matched to afrequency specified by network operation requirements.
 54. Thenon-transitory computer-readable medium of claim 50, wherein the timinginformation is indicative of a phase difference between a first pilotsignal received by the access terminal from the femto cell access pointand a second pilot signal received by the access terminal from anotheraccess point.
 55. The non-transitory computer-readable medium of claim50, wherein the timing information is indicative of a timing differencebetween a time at which a frame from the femto cell access point isreceived by the access terminal and a time at which a frame from anotheraccess point is received by the access terminal.
 56. The non-transitorycomputer-readable medium of claim 50, wherein the acquiring of thetiming information comprises sending a request to the access terminalfor the timing information as a result of the determining that the femtocell access point is communicating over the dedicated channel.
 57. Thenon-transitory computer-readable medium of claim 56, wherein: thecomputer-readable medium further comprises code for causing the computerto estimate a reliability of the clock; the computer-readable mediumfurther comprises code for causing the computer to determine a rate atwhich the timing information should be provided by the access terminalbased on the estimated reliability; and the request for the timinginformation comprises a request for the access terminal to provide thetiming information at the determined rate.
 58. The non-transitorycomputer-readable medium of claim 50, wherein: the timing information isindicative of a timing difference between the femto cell access pointand another access point; the computer-readable medium further comprisescode for causing the computer to determine that the other access pointhas sufficiently accurate timing; and the computer-readable mediumfurther comprises code for causing the computer to elect to use thetiming information received from the access terminal for the adjustingof the clock as a result of the determining that the other access pointhas sufficiently accurate timing.
 59. The non-transitorycomputer-readable medium of claim 50, wherein: the computer-readablemedium further comprises code for causing the computer to determine thatthe access terminal is in idle mode; and the timing information isacquired from the access terminal as a result of the determining thatthe access terminal is in idle mode.